1. Field of the Invention
This invention relates generally to a vehicle seat and more particularly to a seat for use on tractors that has an improved structure for holding the seat upholstery cover and a protective channel shaped finishing strip onto the edge of a seat pan shell.
2. Description of the Prior Art
U.S. Pat. No. 4,561,621, issued Dec. 31, 1985 to Kevin E. Hill, discloses a typical seat assembly which includes a rigid metal seat pan formed to provide seat and backrest portions. A shaped seat and backrest cushion of resilient material is fixed upon the seat pan and fabric upholstery cover is placed over the cushion. The fabric is secured to the edge of the seat pan by a channel shaped finishing strip that is placed over both the edge and the fabric and crimped in place. In the prior art structure, the fabric and channel shaped strip are held in place on the pan by friction between the channel and the surface adjacent the edge of the seat pan.
While this type of prior art seat structure will generally perform satisfactorily, problems can arise under certain use conditions. Tractor seats, for example, are normally subjected to rigorous use and some operators may repeatedly grasp the edge of the seat pan with their hand or hands and then pull to assist themselves in mounting and dismounting the tractor.
This pulling can concentrate extremely high lateral forces on portions of the channel shaped strip that are gripped and result in the strip being pulled off of the seat pan edge. Further, the channel shaped strip is usually bent or otherwise damaged as it is pulled off and cannot be reinstalled. If the channel shaped strip is not replaced, the fabric edge, even if cemented down, will ultimately come loose. Further, with the channel shaped strip removed, the sharp hostile edge of the seat pan is exposed with a potential to injure the seat user. Also, the fabric is free to pull away from the seat cushion to expose the foam or sponge rubber core, which is fragile, and subject to wear and deterioration.
A further problem is that of possible penetration of water into the interface between the cushion and the seat pan. Such water can cause the seat pan to rust if it is made of steel. Further, undue amounts of water can make the seat cushion soggy and possibly cause discomfort to the seat occupant.
When the seat is occupied by unusually large sized persons, prior art seat cushions do not provide as much lateral support and reenforcement for the outer margin of the seat cushion as desired. The formed sides of the seat pan provide some of the lateral or side support. Consequently, the outer margin of the cushion may compress down against the peripheral edge of the seat pan. Such compression can subject the upholstery to sharp folding which shortens its life, especially when vinyl is used, and, further, the peripheral edge of the seat pan is likely to concentrate more pressure to specific body portions in contact therewith than is desired resulting in possible discomfort after sitting in the seat for long periods of time. In the prior art it is known to avoid concentration of pressure on body portions by using oversized, thick, deeply cushioned seats. Such oversized cushions increase the amount of material used and thus significantly increase both the seat cost and its size.
It is possible to secure the channel shaped finishing strip to the seat pan by using closely spaced rivets. This method is labor intensive and costly. Further, it is possible for the heads of the rivets to not be completely seated which can result in the rivet itself presenting a sharp hostile edge.
The problem which has not heretofore been satisfactorily solved is how to provide a compact seat which can be efficiently and correctly assembled with a minimum amount of labor, but which will have provision for quickly and accurately fastening the seat upholstery and a channel shaped seat pan finishing strip to the seat pan in a manner which will minimize the risk that the strip will be pulled loose even when subjected to unreasonable force; which will provide an improved gasket effect to minimize risk of water penetrating between the seat pan and the seat cushion; and which, in addition, will provide lateral body support without the necessity of providing an oversized seat cushion so that the size, weight and cost thereof can be kept to a minimum while still providing comfort and support to the seat occupant.